Method of dyeing aquagel acrylonitrile polymer fibers by stretching in a heated aqueous dye bath



United States Patent METHOD OF DYEING AQUAGEL ACRYLGNI- TRILE PQLYMER FIBERS BY STRETCHlNG IN A HEATED AQUEOUS DYE BATH Allan R. Wirth, Williamshurg, Va., Stanley A. lvlurdoek, Concord, Caliil, and Geerge B. Berry, Parltershurg, W. Va, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Apr. 14, 1961, Ser. No. 162,921 9 Claims. (Cl. 855) This invention contributes to the synthetic fiber art and has particular reference to the dyeing of synthetic fibers. Particularly, it relates to a method of dyeing wet-spun acrylonitrile polymer fibers while they are in a freshly formed gel condition.

Synthetic fibers, including acrylonitrile polymer fibers,

1 have always been diificultly dyea ble in contrast to the \commonly available natural fibers, i.e., cotton and wool. Several methods of approach have been pursued in attempting to solve the inherent and attendant difficulties encountered with acrylonitrile polymer or acrylic fiber dyea'bility. Among these have been the development of dyestulls or particular dyeing procedures specifically designed for or especially suited to the polymer structure. Other schemes included building into the polymer structure sites which are receptive to dyestuffs such as might be accomplished by certain additaments that are copolymerized with acrylonitrile to fiber-forming polymers, or incorporated in the acrylonitrile polymer by blending and the like.

Although the foregoing means have frequently led to better dyed or dyeable fibers, usually, more tedious and cumbersome techniques are required and thus are more costly than normally operated procedures for which dye houses are equipped. Or, particularly when dye-assisting additaments are incorporated in the fiber-forming polymer through copolymerization and so forth, there is a sacrificial loss in some of the inherent properties so desirable in the polyacrylonitrlile backbone. Even when improved dyeability is obtained, the inability to attain through-dyed fibers has frequently persisted.

Another method sometimes employed is to add color, generally in the form of a pigment, into the spinning solution, frequently called spinning dope. This method, however, has the inherent disadvantage of contaminating the polymer handling and conveying systems with colored bodies which must be dealt with when plain white fibers are desired.

Another method of dyeing 'acrylonitrile polymer fibers that have been spun from certain aqueous salt solutions has been proposed in US. Patent No. 2,558,735. The patent describes a method of dyeing the acrylonitrile polymer fibers while they are in the form of a gel structure. The present invention also relates to a method of dyeing acrylonitrile polymer gels.

It is the chief aim and concern of the present invention to provide an improved and highly efficient method for dyeing acrylonitrile polymer gel fibers whereby fibers are uniformly and continuously obtained having excellent shades of coloration, dye penetration, and fastness properties. This and related objects will be manifest in the ensuing disclosure and specification In accordance with the present invention, a method is provided for dyeing acrylonitrile polymer gel fibers whereby; 'a fiber-forming acrylonitrile polymer that contains in the polymer molecule at least about 80 weight percent polymerized acrylonitrile, any balance being another copolymerized ethylenically unsaturated monomer that is polymerizable with acrylonitrile, is spun from a solution that is a solvent for said acrylonitrile polymer into an aqueous coagulating bath to form acryloniu'ile polymer filaments; the filaments are Washed essentially "ice free of any residual acrylonitrile polymer solvent; and, said filaments are subsequently simultaneously stretched and dyed while immersed in an aqueous dye bath.

The fibers treated in accordance with the invention possess excellent physical properties in addition to being through dyed to excellent deep shades of coloration and having superior resistance to fading from exposure to washing and light. The present inventive method provides a highly expedient and efficient means for continuously, uniformly and reproducibly dyeing acrylonitrile polymer fibers employing a wide variety of dyestuffs.

The invention is applicable to the dyeing of acrylonitrile polymer fibers which are fabricated from fiber-forming acrylonitrile polymers that contain in the polymer molecule at least about weight percent of acrylonitrile, especially polyacrylonitrile, which are wet spun in and with systems that are adapted to utilize aqueous coagulating liquids for the spinning operation, such as systems wherein ethylene glycol, dimethyl formamide, dimethyl sulfoxide, butyrolactone and the like or the various aqueous saline polyacrylonitrile-dissolving solvents are employed as spinning solution solvents for the polymer and are also present in non-polymer-dissolving quantities in the aqueous coagulating liquid used in the spin bath.

The utile, known aqueous saline solvents for the various fiber-forming acrylonitrile polymers and polyacrylonitrriile include zinc chloride, the various thiocyanates such as calcium, lithium bromide, salt mixtures of the socalled lyotropic series, and others recognized by the art, as has been disclosed, among other places, in United States Letters Patents Nos. 2,140,921; 2,425,192; 2,648,- 592; 2,648,593; 2,648,646; 2,648,648; 2,648,649; and 2,949,435. Advantageously, aqueous zinc chloride solutions are used for the purpose.

After acrylonitrile polymer fibers have been wet spun they are most frequently water washed to remove any residual polymer solvent from the freshly formed filaments, thus forming an intermediate fiber product often referred to as a gel or aquagel filament. Thoroughly washed acrylonitrile polymer aquagel fibers, incidently, are usually found to contain not more than 5.5 parts by weight of water (including residual extrinsic or exterior water associated therewith) for each part by weight of dry polymer therein. More frequently, washed acrylonitrile polymer aquagel fibers are found to contain from about 2 and usually from about 3 to 4 parts by weight of Water for each part by weight of polymer.

The present invention takes advantage of an improved method of dyeing acrylonitrile polymer fibers while providing another essential treatment to the fibers during the manufacture. As is well known, in order to provide fibers having suitable physical properties they are necessarily stretched or oriented to some predetermined degree. Thus, this invention combines a fiber stretching treatment with a fiber dyeing treatment without one taking away or having any deleterious effects on the other. Indeed, to the contrary, excellent and more efiicient dyeing of the fibers is afforded by this invention not only from the standpoint of dyed properties but also from the standpoint of ease of control, uniformity of product, and the extremely short dyeing times required :to dye the fibers to deep, level and through-penetrated shades. Further, the invention possibilitates a dyeing process without the need for incorporating any significant additional equipment other than that which is encountered in a normal wet-spinning operation.

It is of particular significance that the present invention takes advantage of a feature entirely out of keeping to known dyeing behavior and techniques. This is based on the finding that dyeing of the acrylonitrile polymer aquagel filaments is actually enhanced by decreased dyeing times. Specifically, the dye pick-up by the aquagel '3 filaments is increased with an increase in stretch-ratio applied to the filaments while in the dye bath. This results in a decrease in residence time of the filaments in the dye solution.

In the practice of the invention, after the acrylonitrile polymer fibers have been wet spun and washed essentially free of any residual polymer solvent, the gel or aquagel filaments are subjected to a drawing, stretching or orienting sequence in an aqueous bath or baths, generally heated between about 70 and 110 C., and advantageous- 1y between about 90 and 100 C., in which is mixed the desirable water-soluble or Water-dispersible dye. The aquagel filaments prior to entering the hot stretch-dye baths are for the most part substantially unstretched, although it is not objectionable and is sometimes desirable for a slight or partial stretch to be imparted to them before the dye-stretch bath.

As indicated, the stretching-dyeing combination may be accomplished in one or a series of two or three or more baths. Ordinarily, the total combination of stretches given to the filaments, which combination of stretching may involve stretching preceding, or after, and always during the dyeing of the filaments, is enough to stretch the filaments about 10 to 14 or so times their length on emerging from the coagulation bath.

Generally, optimum results in dyed properties are obtained when the aquagel filaments are given a maximum stretch in the dye bath. Beneficially, the stretch ratio used to stretch the filaments while in the dye bath is between about 15:1 and the stretch ratio that will cause rupture of the filaments at the bath temperature employed, and advantageously between about :1 and :1. As mentioned, although the dye-stretch operation may be applied to the filaments in a series of dye baths, excellent results are obtained when the dye-stretch treatment is accomplished in a single dye-stretch bath.

The invention encompasses certain other modifications in cooperation with imparting a simultaneous dyeingstretching treatment in order to obtain highly advantageous dyeing rates, dye pick-up and excellent dyed properties. Thus, the effects of stretching the aquagel filaments prior to entering the dye-stretch bath and of temperature pretreating the aquagel filaments prior to entering the dyestretch bath have corollary additive or diminishing results on the dyeing process.

It is desirable and advantageous that the filaments entering the dye-stretch bath have been given but little or no stretch. Ordinarily, it may be necessary to cold stretch the filaments after leaving the coagulation bath and prior to entering the dye-stretch bath in order to provide the aquagel filaments with enough strength to withstand the subsequent handling. In the practice of the present invention, it is preferable that the stretch ratio used to stretch the aquagel filaments at any point after leaving the coagulation bath and prior to entering the dye-stretch bath be not in excess of about 1.6: 1.

Advantageously and beneficially, the aquagel filaments are heat pre-treated prior to being subjected to the simultaneous dyeing-stretching operation. This heat pretreatment may be accomplished by exposing the filaments to temperatures ranging from about 70-l10 C. Generally, the'heating medium is a fluid aqueous medium such as water or steam. Preferably, a liquid aqueous bath is employed.

The dyestuffs that are beneficially employed in the practice of the present invention may be selected from any of a number of dyestuif classes. Generally, all watersoluble and water-dispersible dyes including pigments may be employed with advantage. Specifically, among these-are mentioned the vat, direct, metallized, basic, acid, azoic, acetate, reactive, ingrain and the like classes of dyestufis.

Depending on the particular dyestuff employed and other conditions, the concentration of the dye in the dyestretch bath may be as little as 0.001 weight percent,

based on the weight of the solution, up to the saturation concentration, either solution or dispersion, of the dye in water or until normal operation would be afiected by such things as agglomeration and the like. Normally, for a given set of conditions the amount of dyestuft picked-up by the filament increases as the concentration of the dyestufi in the dye-stretch bath increases.

As previously discussed, the invention is particularly applicable to dyeing acrylonitrile polymer aquagel filaments. These may be spun from homopolymer-ic acrylonitrile or from acrylonitrile polymers containing at least about weight percent of acrylonitrile, any balance being another monoethylenically unsaturated monomer copo'lymerizable with acrylonitrile. Exemplary of some of the other monomeric materials which may be employed advantageously with acrylonitrile in the practice of the present invention include allyl alcohol, vinyl acetate, acrylamide, methacrylamide, methyl acrylate, 2-vinyl pyridine, dimethylaminoethylacrylate, methacrylonitrile, acrylic acid, itaconic acid, vinyl acetic acid, ethyl acrylate, fumaronitrile, 2-vinyl 5- ethyl pyridine, ethylene sulfonic acid and its alkali metal salts, allyl sulfonic acid and its alkali metal salts, vinyl lactams such as vinyl caprolactam and vinyl piperidone, vinyl benzene sulfonic acid and its salts, vinylbenzene-trimethyl ammonium chloride, vinylmethyl ether, N-acryloyl taurine and its salts, 2-amino-ethyl-methaerylate hydrochloride, Z-sulfoethylacrylate, 2-sul-fopropylacrylate, maleic anhydride and the like, including mixtures thereof.

As has been indicated, when acrylonitrile polymer, particularly polyacrylonitrile, fibers are being manufactured zinc chloride may most advantageously be utilized as the sole, or at least the principal, saline solute in the spinning solvent employed for the polymer. In such instances, the aqueous solution of zinc chloride in the spinning solution may advantageously be in a concentration of from 55 to 65, preferably about 60 percent by weight, based on the weight of the aqueous solution. The quantity of substantially pure water passed countercurrent to the filaments in the chamber should be sufiicient, when such aqueous zinc chloride solvent spinning solutions are employed, so as to maintain the concentration of zinc chloride in the portion of the liquid in the spinning zone at a non-polymerdissolving coagulating concentration of at least about 25 percent by weight; advantageously from about 30 to 50 percent by weight, and preferably between about 40 and 45 percent by weight. In such aqueous zinc chloride systems for acrylonitrile polymers, wherein the freshly wet spun polymer is generally obtained in an aquagel form, it is generally desirable for the spinning solution that is extruded to contain between about 4 and 20 percent by weight of dissolved polymer; more advantageously from about 6 to 15 percent by weight of dissolved polymer; and preferably, particularly when polyacrylonitrile fibers are being manufactured, from about 8.5 to 11.5 percent by weight of fiber-forming polymeric solids in the spinning solution.

Aqueous zinc chloride spinning solutions of fiber-forming acrylonitrile polymers are beneficially extruded at a spinning temperature of from 0 to 50 0; preferably from about 10 to 30 C., into an aqueous zinc chloride coagulating liquid that is maintained at a coagulating temperature of from 0 to 30 0; preferably from about 10 to 20 C.

After the aquagel filaments have been dyed in the dyestretch pans following the practice of the present invention, they may be subjected to further treatments common to wet spinning processes such as heat treating, crimping, drying, etc.

By way of further illustration of the invention, the following examples are presented in which all parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 A spinning solution comprised of about 10 parts of fiber-forming polyacrylonitrile having an average molecular weight of about 35,000 dissolved in about 90 parts of a 60 weight percent aqueous solution of zinc chloride was extruded through a 300 hole, mil/hole diameter spinnerette into about a 43 weight percent aqueous solution of zinc chloride at about 14 C. After washing the aquagel filaments free of ZnCl with distilled water, the gel was given a 1.4:1 cold stretch in air at ambient temperature, and then passed through two sequential boiling aqueous dye-stretch baths. The first of the dye-stretch baths contained a 0.5 weight percent dye solution of Bcllfast Red LRF (no Colour Index) based on the weight of the solution, and the second dye-stretch bath contained about a 0.05 weight per cent solution of the same dye. The oriented and dyed filaments were then passed through a cold washing pan (distilled water at ambient temperature) no stretch being imparted, and then briefly through an aqueous 0.5 weight percent solution of Surfynol 102 (4,7 dimethyl-5-decyne-4,7-diol) which serves as an opening agent. The fiber was then dried in a relaxed form at 140 C. for 7 /2 minutes in air using a continuous belt oven. Two different samples were prepared in this manner ditfering only in the stretch imparted to the filaments while in the dye-stretch baths. The results are presented in Table I.

1 Based on the depth of shade (as measured from reflective spectrophotometric results) of the lowest stretch ratio: 100.

Thus, it may be seen from Table I that reduction of the residence time in the hot stretch pan by a factor of about two and one-half times actually resulted in a 25 percent increase in color depth on the finished fiber.

EXAMPLE 2 Following the general procedure of spinning the polyacrylonitrile aquagel filaments described in Example 1, several samples were prepared by dyeing the filaments in a single dye-stretch pan. The stretch given the filaments in the boiling dye solution in the dye-stretch pan was varied as was the stretch given the filaments in a succeeding boiling water bath. The coagulation bath temperature was maintained at C., and the filaments were given a 1.45:1 cold stretch prior to entering the dyestretch bath.

The dye solution in the dye-stretch bath was a 0.02. weight percent solution of Anthraquinone Green GNN (Colour Index Acid Green 25). The concentration of dye in the dye-stretch bath was controlled using a Beckman DK-Z spectrophotometer as a color sensing device. A side stream of dye solution was removed from the dyestretch bath and cycled through a continuous flow spectrophotometr-ic cell. When a change in dye concentration occurs, the absorption measured by the spectrophotometer changed accordingly. The change in spectrophotometer reading was picked up electronically and an impulse opened a solenoid valve which allowed dye solution to flow into the dye-stretch solution.

'Ihe amounts of dyestutr actually picked up by the filaments was determined by dissolving the finally dried fibers in dimethylformamide and analyzing for the amount of dyestuff in the fibers through spectrophotometric absorption data obtained with the use of a Beclcman DK-2 spectrophotometer. The amount was recorded as weight percent dye based on the fiber dry Weight. The results are presented in the following tabulation.

Table I1 Stretch Ratio Stretch Ratio Weight Per- Sample in Dyein Succeeding cent Dye Stretch Bath Aqueous Bath in Fiber EXAMPLE 3 Using the procedure of Example 2, a series of samples were produced deviating from the method of Example 2 in that the filaments after being cold stretched were stretched in a boiling water bath before entering the dyestretch bath, and that no further stretch was given the filaments after leaving the dye-stretch bath. Following this procedure, another series of samples were made excepting to use a coagulation bath temperature of 55 C. Table 111 is a summary of the results.

Another group of samples was prepared according to the procedures of Examples 2 and 3 excepting to use a 0.5 weight percent solution of the dye in the dye-stretch bath. A coagulation bath temperature of about 15 C. was used for all samples. The results are indicated in the following table.

Table IV Stretch Stretch Stretch Weight Ratio in Ratio in Ratio in Percent Sample Preceding Dye- Succeeding Dye in Aqueous Stretch Aqueous Fiber Bat Bath Bath EXAMPLE 5 Another series of samples were made according to the foregoing procedure except that the cold stretch given to the aquagel filaments prior to entering the dye-stretch bath was changed. These results are listed below.

Table V Stretch Stretch Weight Cold Ratio in Ratio in Percent Sample Stretch Dye- Succeeding Dye in Ratio Stretch Aqueous Fiber Bath B h EXAMPLE 6 Polyacrylonitrile spinning solution produced as in Ex- Table VI is a tabulation of the excellent results obtained with this procedure using a wide variety of dycstufi classes.

Table VI Washiast- Dyestufi Type Color Index ness Lightrast- AATOO ness, hr.

Rat.

Bellelast Red LRF No 4 100 Chlorantine Fast Rubine RNLL D rect Red 107--.. 4 100 Diphenyl Fast Bordeaux 30.. Direct Red 86- 5 Arilite Blue LDL None 4 100 duPont Anthraquinone Blue All... 0 109 duPont Anthraquinone Green GNN do o 4 100 Chlorantiue Fast Turquoise VLL Direct Direct Blue 86.... 4 100 Superlitelast Blue GL o Direct Blue l00 4 Renclar Brilliant Blue B Acid None 3 100 Acid II. Scarlet GL Newdo do 4 40 Brilliant Alizarine Millilla Red FBL do Acid Red 143 4 100 Superlitefast Red GL 5 00 Sulfonic Acid Blue B d o 5 0 Lanasyn Blue GL Acid Blue 127 4 10;

Lanasyn Yellow GL.. do Acid Yellow 114..- 5 100 Irgalall Brilliant Green 3 GL do None 4 0 Graphtol Blue Pigment.. do 4 100 Gycolan Yellow BEL cone Acid Acid Yellow 54...- 5 100 Premet. Neopilate ellOWG Neut. None 4 100 Premet. Cibaeron Brilliant Red 3 B Rgactivenu 0 4 100 Cibacron Turquoise Blue G 4 100 Procion Turquoise HG 4 100 Cibacron Blue 3 G 5 100 Oibacron Brilliant Yellow 3 G. 1 5 8O GYCOM R G Acid Red 183 5 100 Gycolan Blue GGL. do Acid Blue s 5 100 Blue R9118. CF do None 4 100 Gycolan Green BFL .1- 1 Acid Green 12 4 100 Palatine Fast Blue RRNA-CF Acid Blue 154 5 100 Gyoolan Navy B1116 RL None 5 0 Gycolan Brown BBL- 5 100 Neolan Violet l R. undo 5 100 Acid Orange 62 5 100 Acid Red 192 5 100 Acid Red 212 5 100 Acid Red 186 5 10 4 80 5 100 5 100 5 100 5 100 5 100 Acid Violet 56- 4 100 Acid Brown 97 4 80 None. 5 100 Acid B 5 Eastman Fast Yellow 8 GLF None 5 2O Genacryl Brilliant Red B 4 40 Washiastness was determined by washing the dyed samples with a neutral soap for 30 minutes at 160 F in a Laundrometer and compared by AATCC washfastness ratings, 54-3-2-1-0, the higher the number the better the Washfastness.

the indicated hours.

ample 1 was spun through a 500 hole, 8 mil/hole diameter spinnerette into an aqueous 43.0 percent ZnCl coagulation bath at 14 C. Adter washing the aquagel filamerits free of ZnCl with distilled water, the gel was given a 1.4:1 stretch in air at ambient temperature, followed by a 3.75:1 stretch through a boiling 0.5 percent dye solution and then a 2.63:1 stretch through a boiling 0.05 percent dye solution for a total of 13.5 :1 total stretch ratio. The oriented, dyed tow was then passed through a cold washing pan (distilled water at ambient temperature), no stretch being imparted, and then briefly through a /2 percent Surfynol 102 solution which serves as an opening agent. The fiber was then dried in a relaxed form at 140 C. for 7 /2 minutes in using a continuous belt oven.

The residence times of the aquagel filaments in the dye- A typical set of physical properties of fibers produced by this procedure is as follows:

Tenacity Elongation Yield Denier Gms./ Den. Percent Gms. Den. 2.8 3 .5 3 1 1.00

No break in color shade was observed at EXAMPLE 7 A spinning solution comprised of 10 parts of fiberforming polyacrylonitrile having an average molecular weight of about 35,000 dissolved in about parts of a 60 percent aqueous solution of zinc chloride was extruded through a 300-orifice spinnerette, each orifice having a l5-mil diameter, into an aqueous coagulating bath that contained about 43 percent by weight zinc chloride to form about a 5400 denier tow. The temperature of the coagulating bath was 15 C. The coagulated tow was washed substantially free from salt after being withdrawn from the coagulating bath and was then passed through two pans each containing an aqueous dye bath. Of 54 gram of Alcian Blue 8 GN ((3.1. 165001) and 50 grams of Alcian Blue 8 GX (C.I. 165008), 7 of the combined total was placed in the first pan and A in the second pan to give about a 0.36 weight percent dye solution of the dyestuff in the first pan and about a 0.07 weight percent dye solution in the second pan. The temperature of the baths was maintained at C. The aquagel filaments were stretched 2.5-4.5 times in the first bath and about 1.6 times in the second bath. The filaments were then passed through two more hot aqueous baths where they were stretched (1.6:1 and 1.13:1) so the ultimate stretch ratio given to the fibers was about 13:1. The total residence time of the aquagel filaments in the dye solutions was 12-13 seconds.

The dyed fiber was tested for Washiastness by washing with a neutral soap (Lux) in a Laundrometer for 30 minutes. Tests were run at 140 F. and 160 F. with and without 3 percent, based on the fiber dry weight (OWF), Gycofix 100 (a fixing agent). The Gycofix 100 is used as an after-dyeing treatment on the fiber. Excellent washfastness was observed in all four tests. Also, good lightfastness was observed on the dyed sample after 60 hours exposure in a Fadeometer.

A similar run was made with a difierent dyestuif and dye concentration in the dye-stretch pans. These results are given in Table VII including dye penetration into the fibers which was determined by microscopic observation of fiber cross-sections.

polymer aquagel filament is stretched while immersed in said aqueous dye bath between about 5 and 10 times the length said filament had before it entered said aqueous dye bath.

3. The method of claim 2, wherein said stretching of said acrylonitrile polymer aquagel filament in said aqueous dye bath is accomplished by imparting a portion of said stretch to said filament in each of a series of at least two adjacent aqueous dye baths.

4. The method of claim 1, wherein said wet-spun acrylonitrile polymer aquagel filament before entering said aqueous dye bath has not been stretched more than about 1.6 times the length said filament has when it emerges from the acqueous coagulating bath in which said aquagel filament is coagulated from said solution of an acrylonitrile polymer.

Dye Bath Cone, Wt. Light Test Fiber Dye Color Type percent Dye 140" 140 160 160 Denier Index Pentr.

40 hr. 60hr. Paul Pan2 '17 Proeion Scarlet {13G 161016 Reactive.-

pus Cibacron Brilliaiut Red 313 none" d0 pus Procion Brilliant Orange HGR (Mixture) 162002 do 0.67 0.14 Through Fair--. Good" Fair Good Good. Good.

a Without after treatment of Gycofix 100 (3% OWF).

b With after treatment of Gycofix 100 (3% OWF).

It is to be understood that certain modifications and alterations of the herein specifically delineated embodiments of the invention can be entered into without departing from the intended spirit and scope of the invention. Therefore, the invention is to be interpreted in terms of the hereto appended claims.

What is claimed is:

1. In a method of dyeing an acrylonitrile polymer aquagel filament that has been wet-spun from a solution of an acrylonitrile polymer that contains in the polymer molecule at least 80 weight percent polymerized acrylonitrile, any balance being another copolymerized ethylenically unsaturated monomer that is polymerizable with acrylonitrile, the improvement which comprises continuously passing said aquagel filament through an aqueous dye bath maintained at a temperature between about 70 and 110 C. and while immersed in said aqueous dye bath stretching said aquagel filamentat least about 1.5 times the length said filament had before it entered said aqueous dye bath.

2. The method of claim 1, wherein said acrylonitrile 5. The method of claim 1, wherein said acrylonitrile polymer aquagel filament is heated to between about and 110 C. before entering said aqueous dye bath.

The method of claim 1, wherein said acrylonitrile polymer aquagel filament is heated to between about and C. before entering said aqueous dye bath.

7. The method of claim 1, wherein the temperature of said aqueous dye bath is maintained between about 90 and 100 C.

8. The method of claim 1, wherein said acrylonitrile polymer is polyacrylonitrile.

9. The method of claim 1, wherein said solution of an acrylonitrile polymer is an aqueous zinc chloride solution of an acrylonitrile polymer.

References Cited in the file of this patent UNITED STATES PATENTS Cresswell et a1. July 3, 1951 Cresswell July 3, 1951 Mautner June 20, 1961 

1. IN A METHOD OF DYEING AN ACRYLONITRILE POLYMER AQUAGEL FILAMENT THAT HAS BEEN WET-SPUN FROM A SOLUTION OF AN ACRYLONITRILE POLYMER THAT CONTAINS IN THE POLYMER MOLECULE AT LEAST 80 WEIGHT PERCENT POLYMERIZED ACRYLONITRILE, ANY BALANCE BEING ANOTHER COPOLYMERIZED ETHYLENICALLY UNSATURATED MONOMER THAT IS POLYMERIZABLE WITH ACRYLONITRILE, THE IMPROVEMENT WHICH COMPRISES CONTINUOUSLY PASSING SAID AQUAGEL FILAMENT THROUGH AN AQUEOUS DYE BATH MAINTAINED AT A TEMPERATURE BETWEEN ABOUT 70* AND 110*C. AND WHILE IMMERSED IN SAID AQUEOUS DYE BATH STRETCHING SAID AQUAGEL FILAMENTAT LEAST ABOUT 1.5 TIMES THE LENGTH SAID FILAMENT HAD BEFORE IT ENTERED SAID AQUEOUS DYE BATH. 